The sum of which two types of angles is exactly 180 degrees?

The correct answer is the type of angles known as supplementary angles. By definition, supplementary angles are two angles whose measures add up to exactly 180 degrees. This property makes them particularly useful in various geometric situations and problem-solving scenarios. For instance, if one angle measures 110 degrees, its supplementary angle would measure 70 degrees, since 110 + 70 = 180.

The other types of angles mentioned do not share this property. Complementary angles, for example, add up to 90 degrees rather than 180. Acute angles are angles that measure less than 90 degrees, and reflex angles measure more than 180 degrees but less than 360 degrees. Thus, it is the supplementary angles that precisely sum to 180 degrees, fulfilling the requirement of the question.